As John Travolta celebrated his 60th birthday on Feb. 18, the actor was sorely missing his late son, Jett. During a recent on-stage interview at the Theatre Royal Drury Lane in London (published by the BBC on Feb. 17), Travolta called his son's death "the worst thing that's ever happened in my life."

"The truth is, I didn't know if I was going to make it," the "Savages" actor shared. "Life was no longer interesting to me, so it took a lot to get me better."

Travolta and wife Kelly Preston's eldest son, Jett, died suddenly at the age of 16 in January 2009 from a seizure while on a family vacation in the Bahamas. Jett had a history of seizures and was autistic. Travolta and Preston, 51, are also parents to daughter Ella, 13, and son Benjamin, 3.

After Jett's death, Travolta said he "didn't want to wake up," but credits his religious faith and fellow members in the Church of Scientology with helping him cope. "I will forever be grateful to Scientology for supporting me for two years solid, I mean Monday through Sunday," Travolta explained during the talk. "They didn't take a day off, working through different angles of the techniques to get through grief and loss, and to make me feel that finally I could get through a day."

In addition to having the support of Scientology, which he has practiced since 1975, Travolta told "Good Morning America" last June that late actor James Gandolfini was also by his side during that difficult time. "James went out of his way to come to Florida and he would not leave Florida until I was okay, or he felt that I would be fine," Travolta said of his "Get Shorty" and "Lonely Hearts" co-star.

Gandolfini died suddenly of a heart attack at the age of 51 in June 2013. Travolta told "GMA" he is going to make sure his friend's family -- wife Deborah Lin, son Michael and baby daughter Liliana -- are taken care of in the future. "My goal is to make sure that his family is okay," he said. "His little boy, I watched him grow up, and his brand new little girl. We'll just make sure they're taken care of. That's the whole idea."